Lewis’ Woodpecker Melanerpes lewis
Lewis’ Woodpecker is an uncommon winter visitor to San Diego County. It occurs mainly in the mountains and foothills, seeking large trees at the edges of meadows or scattered in grassland. Its distribution is patchy, the birds often recurring year after year at favored spots while ignoring other habitat that looks similar. On the other hand, the numbers wintering in San Diego County vary greatly from year to year, and in irruption years occasional birds reach the coast or the desert floor.
Winter: Oak savanna and mountain meadows constitute the main habitats for Lewis’ Woodpecker in San Diego County. The species occurs mainly above 1000 feet elevation, rarely within 20 miles of the coast. From 1997 through 2002, our highest counts were of eight at San Ignacio, Los Coyotes Indian Reservation (E21), 19 December 1999 (M. C. Jorgensen), seven at Lake Cuyamaca (M20) 11 February 1999 (D. Aklufi), and eight in upper McCain Valley (R26) 23 January 2000 (J. R. Barth). In irruption years, however, numbers can be much larger. Totals on the Lake Henshaw Christmas bird count vary from zero in 1991 and 1992 to 45 on 29 December 1981. On the Escondido count, Lewis’ Woodpecker has been recorded on only three of 17 counts from 1986 to 2001, yet the count on 30 December 1989 yielded 36. The largest number ever reported in San Diego County was at least 60 on Palomar Mountain 26 October 1982 (R. Higson, AB 37:225, 1983).
During the atlas period our winter record nearest the coast was of one about 9 miles inland at Case Spring, Camp Pendleton (B4), 17 December 2000 (P. A. Ginsburg). Most of the few sightings along the coast are during migration periods. Lewis’ Woodpeckers, single individuals in all cases, have been found just twice on the Oceanside Christmas bird count (1 January 1979, 21 December 2002), once on the Rancho Santa Fe count (16 December 1984), and once on the San Diego count (16 December 1989). The only records from the Anza–Borrego Desert are of one at Peña Spring and in Culp Valley (G23/H23) 26 September and 6 November 1991 (M. L. Gabel) and of up to three at Club Circle, Borrego Springs (G24), 31 October 1989–17 April 1990 (A. G. Morley et al.).
Migration: The arrival and departure of Lewis’ Woodpecker in San Diego County vary greatly from year to year. Fall arrival is generally in late September or early October; 15 September (1950, one at Palomar Mountain, E. Beemer) is the earliest recorded date. In 1998 the latest report was on 8 February, but in 1999 it was 24 April, in 2000 it was 1 June, and in 2001 it was 6 May. The occurrence on 1 June 2000 was the latest ever for San Diego County; on that date a Lewis’ Woodpecker got trapped and died in the shed for donations to the Salvation Army in Descanso (P20; G. Wynn, SDNHM 50439).
Acorn Woodpecker Melanerpes formicivorus
The Acorn Woodpecker is famed for its unique habit of storing acorns in granary trees, which the birds may riddle with thousands of holes. It will also store acorns in utility poles, the walls of wooden buildings, and boulders composed of soft granite. Its communal breeding and social life have attracted intensive study, leading to new perspectives on animal behavior. With acorns so important in its diet, the woodpecker is intimately linked with oak woodland. In San Diego County it is common year round wherever there are extensive groves of oaks.
Breeding distribution: The Acorn Woodpecker’s distribution in San Diego is essentially the same as that as oak woodland. The habitat can be groves of the coast live oak only, riparian woodland containing some oaks, or montane forest in which the black, canyon live, and coast live oaks are mixed with conifers. The latter may be superior habitat, as pine trees, with their softer bark, make better granary trees than oaks, in which the woodpeckers typically drill granaries in dead snags only. Also, the tannin content of canyon live oak acorns is less than that of coast live oak acorns, making the former a superior food (Koenig and Heck 1988, Koenig 1991). Our highest estimates of Acorn Woodpecker numbers were all from mixed montane forest, up to 100 as in Palomar Mountain State Park (E14) 17 May 1997 (K. Messer, R. Turner), in Cuyamaca Rancho State Park (N20) 17 July 2000 (B. Siegel), and around Mount Laguna (O23) 6 June 1998 (A. Klovstad, C. Mann). With decreasing elevation, the Acorn Woodpecker becomes less common and more localized, in tandem with oaks. The range approaches within 3 miles of the coast along San Onofre Creek (D2; up to four on 31 March 2001, R. E. Fischer), then contracts inland toward the south. Outlying locations toward the south are Los Peñasquitos Canyon (up to 22 in square N9 on 15 June 1997, L. D. and R. Johnson; up to 6 in square N8 on 2 May 1999, P. A. Ginsburg), San Clemente Canyon (P8; up to three on 27 April 1999, M. B. Stowe), and Tecolote Canyon (Q8/Q9; up to four on 8 August 1998, E. Wallace).
A unique outlying colony of the Acorn Woodpecker is in Quail Botanical Gardens, Encinitas (K7), a completely man-made woodland outside the species’ natural range. Counts here during the breeding season averaged 13 birds (R. and A. Campbell). At Quail Gardens, the tree supplying the woodpecker’s acorns is an Old World species, the cork oak.
The eastern edge of the Acorn Woodpecker’s range tracks the eastern edge of the range of the coast live oak almost exactly, though the birds are lacking from small isolated groves. The easternmost point in San Diego County where the species is resident is at the south end of McCain Valley Road, at the junction with old Highway 80 (west edge of T27; up to three on 3 July 2000, J. K. Wilson).
Nesting: In California, most Acorn Woodpeckers live in groups, in which both sexes share mates and a single nest cavity. Koenig and Mumme (1987) studied the woodpecker’s unusual sex life extensively, putting it in its ecological context. The species’ nest holes, though, are typical of the family, bored on the underside of slightly angled trunks or branches. Atlas observers noted nests in power poles and snags of pine and white alder, as well as coast live, black, and Engelmann oak. In Quail Gardens, K. L. Weaver found nests in a dead palm and a dead pine.
Our observations show that in San Diego County the Acorn Woodpecker usually begins egg laying in early April and continues through mid June. A few suggest laying in late March; a record of fledglings at Live Oak Park (D8) 23 April 1998 (M. Freda) implies laying by 12 March, earlier than the earliest date of 17 May for the well-studied Hastings Reservation, Monterey County (Koenig et al. 1995).
Migration: The Acorn Woodpecker is nonmigratory, rarely appearing outside its breeding range. There is little if any seasonal pattern to these wanderers, which crop up in the middle of the breeding season as often as in fall and winter. Most records of them are within 5 miles of sites where the species is resident. But there are at least 15 records from Point Loma, most of single individuals, though five were there 15 September–15 October 1987 (R. E. Webster, AB 42:136, 1988). Only one Acorn Woodpecker has been noted on the coastal slope as far from the breeding range as the Tijuana River valley, on 10 September 1972 (AB 27:122, 1973).
Similarly, a few Acorn Woodpeckers have been noted on the east slope of San Diego County’s mountains, east of the oaks. On or near the desert floor there are only three records, of one at Lower Willows (D23) 26 June 1988 (A. G. Morley), one near Barrel Spring in the Ocotillo Wells off-road vehicle area (H29) 10 June 1987 (A. G. Morley), and one at the former Fish Creek Ranger Station (L29) 15 May 1973 (ABDSP database).
Winter: The Acorn Woodpecker’s distribution and abundance in winter do not differ materially from those in the breeding season. Our highest winter count was of 175 in Pine Hills (K19) 6 Feb 1999 (S. E. Smith, D. W. Au).
Conservation: There is no evidence for any change in the Acorn Woodpecker’s status in San Diego County through recorded history. The species tolerates low-intensity development of its habitat provided oaks are left undisturbed. Whether such development is compatible with the long-term regeneration of oak woodland, however, is another question. The woodpeckers sometimes take over wooden buildings as granary sites, much to the consternation of the building’s human owners. The population at Quail Gardens appears to represent the only instance of Acorn Woodpeckers colonizing an artificial habitat in San Diego County. The birds there rely, however, on dead branches and trees that will have to be removed. The natural processes of tree death and decay that provide the Acorn Woodpecker with nest sites may be incompatible with the intensive management a botanical garden requires. The drought of 1999–2004 left many oaks in San Diego County stressed or dead, suggesting that climate change leading to a drier climate could affect the Acorn Woodpecker adversely.
Taxonomy: Acorn Woodpeckers resident in San Diego County and elsewhere in California are M. f. bairdi Ridgway, 1881, larger and heavier billed than the subspecies east of the Colorado River.
Gila Woodpecker Melanerpes uropygialis
The Gila Woodpecker reaches the northwestern tip of its range in the Imperial Valley. In San Diego County there were only unsubstantiated reports until 2003–04, when one spent the winter in Borrego Springs. Although the Gila Woodpecker is common in the towns of Brawley and El Centro, the dying off of cottonwood trees in the Imperial Valley disfavors the woodpecker from spreading.
Winter: San Diego County’s first well-supported Gila Woodpecker appeared in a residential area of Borrego Springs (G24) 25 September 2003–1 March 2004 (P. D. Jorgensen), to be observed and photographed by many. The report of one near Jacumba (U28) 17 October 1952 (Gardner 1959) was based on a recollection several years old, and the report of one at Tamarisk Grove 18 January 1986 (Massey 1998) was not substantiated.
Williamson’s Sapsucker Sphyrapicus thyroideus
Though resident in the higher elevations of the San Jacinto Mountains just 15 miles to the north of the county line, and in the Sierra San Pedro Mártir to the south, in San Diego County Williamson’s Sapsucker is a rare winter visitor only. On average, only about one individual is found per year, usually in montane coniferous forest.
Winter: During the atlas period, only four Williamson’s Sapsuckers were found in San Diego County, one near Wynola (J19) 29 December 1997 (J. Alpert), one at Observatory Campground, Palomar Mountain (E14), 24 February 1999 (G. L. Rogers), one along the Azalea Glen Trail, Cuyamaca Rancho State Park (M20) 23 September 2001 (S. Buchanan), and one at 4472 feet elevation in upper Sheep Canyon (C21) 10 February 2002 (L. J. Hargrove, J. Determan). Earlier records are from similar conifer-dominated habitat on Palomar Mountain, at Julian, and in the Cuyamaca and Laguna mountains. The species is usually seen singly, occasionally in twos.
Only seven Williamson’s Sapsuckers have been recorded in San Diego County at elevations below 3500 feet, one at Bonita (T11) 16 December 1968–March 1969 (AFN 23:522, 1969), one near Lakeside (P14) 25 November 1972–1 February 1973 (AB 27:122, 664, 1973), one in La Jolla (P8) 22 November 1989–16 February 1990 (J. Moore, AB 44:162, 330, 1990), and four on Point Loma, 11 October, 15–17 October, and 20–22 October 1987 (AB 42:136, 1988), and 2 December 1996–3 January 1997, Point Loma (V. P. Johnson, NASFN 51:802, 1997). Most of these occurrences at low elevations coincide with irruptions of other montane birds.
Migration: San Diego County records of Williamson’s Sapsucker range in date from 23 September (cited above) and 27 September (1980, Palomar Mountain, AB 35:227, 1981, to 10 April (1979, same locality, AB 33:806, 1979).
Taxonomy: Two subspecies of Williamson’s Sapsucker were long recognized on the basis of a difference in bill size, but they overlap too much for the distinction to be maintained (Browning and Cross 1999, Patten et al. 2003).
Yellow-bellied Sapsucker Sphyrapicus varius
With improved information on the species’ identification, birders are finding the Yellow-bellied Sapsucker to be an annual though rare winter visitor to southern California. At least 25 have been found in San Diego County. Most are immature birds retaining the largely brown mottled head of juvenile plumage.
Winter: Records of the Yellow-bellied Sapsucker are scattered throughout San Diego County, on the coastal slope from Fallbrook (D8) in north (one from 1 December 1984 to 17 February 1985, Fallbrook, R. Higson, AB 39:210, 1985) to Imperial Beach (V10) in the south (one on 18 February 2001, G. McCaskie). But at least ten are from that Mecca for sapsuckers, the Santa Ysabel Mission (I18). Only two have been identified in the Anza–Borrego Desert, both at man-made oases: the Roadrunner Club, Borrego Springs (F24), 6 November 1999, and Casa del Zorro (H25) 4 November 2001 (P. D. Jorgensen).
The historical record for this species is still short, but numbers reaching San Diego County may vary appreciably from year to year. During the five-year atlas period, there were none in 1997–98, six in 1998–99, and one each in the three following years.
Migration: Dates of Yellow-bellied Sapsuckers in San Diego County range from 19 October (1985, one at the Santa Ysabel Mission, C. G. Edwards, AB 40:159, 1986) to 3 March (1998, one in the Tierrasanta area of San Diego, P10, D. K. Adams, FN 52:258, 1998).
Conservation: An apparent increase in Yellow-bellied Sapsuckers wintering in southern California could be a result not only of improved identification criteria but of the breeding range spreading west, into Alaska (Erwin et al. 2004).
Red-naped Sapsucker Sphyrapicus nuchalis
Coming from a breeding range in the Great Basin and Rocky Mountain region, the Red-naped Sapsucker reaches San Diego County as an uncommon winter visitor. It occurs most often in oak woodland but shows up occasionally throughout the county. There is no difference in habitat and behavior between the Red-naped and Red-breasted Sapsuckers here, and the former is only slightly less numerous than the latter. In the lack of previous summer records from southern California, one of the greatest surprises of the atlas field work was three summer observations of the Red-naped Sapsucker from Palomar Mountain, including one of hybridization with the Red-breasted.
Winter: Though the ranges of the Red-naped and Red-breasted Sapsuckers, winter as well as breeding, are largely complementary, in San Diego County both are found in similar numbers in similar areas. The county lies at the northwestern corner of the Red-naped’s main winter range. In the five winters from 1997 to 2002 we recorded the Red-breasted 165 times (183 individuals); we recorded the Red-naped 149 times (180 individuals). Like the Red-breasted, the Red-naped is most frequent in the mountains and wooded canyons in the foothills, as well as in the coastal lowland of northern San Diego County. Our highest daily counts were of four around Sunshine Summit (D17) 23 January 1999 (J. K. Wilson) and four around Santa Ysabel (J18) 14 December 1997 (S. E. Smith). In the south coastal area the species is rare.
With only three, our records of the Red-naped in the Anza–Borrego Desert during the atlas period were even fewer than those of the Red-breasted Sapsucker. Earlier records (Massey 1998, ABDSP database), like these three, are largely from developed areas and oases like Lower Willows.
Migration: The Red-naped Sapsucker occurs in San Diego County mainly from October through March. One in the Borrego Palm Canyon campground (F23) 18 September 1992 (R. Thériault) was early; one at Banner (K19) 18 April 1999 (P. K. Nelson) and one near Jewell Valley (U27) 25 April 1999 (F. L. Unmack) were unusually late.
Breeding distribution: Completely unexpected were three records of the Red-naped Sapsucker from Palomar Mountain in summer. The first was of one paired with a Red-breasted Sapsucker and accompanied by a fledgling just east of Doane Pond (E14) 19 July 1998 (D. S. Cooper). Another, or perhaps the same individual, was in the same area 17 July 1999 (J. R. Barth). Yet another was about 3.4 miles to the southeast in Bull Pasture (E15) 18 June 1999 (C. R. Mahrdt, E. C. Hall). All the birds were observed carefully by observers aware that the species was unexpected for the season. There are no previous records of the Red-naped Sapsucker summering, much less hybridizing with the Red-breasted Sapsucker, in southern California. The mountains of southern Nevada are the nearest point of the species’ traditional breeding range.
Conservation: Numbers of the Red-naped Sapsucker on San Diego Christmas bird counts show a pattern of decrease similar to that of the Red-breasted. The average per count of the Red-naped was 1.4 from 1975 (the first year figures for the two species were consistently listed separately) to 1988 but 0.8 from 1989 to 2001. On counts elsewhere in San Diego County the trend is slight or none. Thus it seems that in spite of the sapsuckers’ feeding on exotic trees, especially the Peruvian pepper, increasing urbanization discourages them.
Taxonomy: The Red-naped, Red-breasted, and Yellow-bellied Sapsuckers were long classified as a single species. Various sources of evidence, however, suggest that they have crossed the threshold of speciation, though the Red-naped hybridizes with both other species along much of the line where their breeding ranges abut (Johnson and Zink 1983, Johnson and Johnson 1985, Cicero and Johnson 1995).
Red-breasted Sapsucker Sphyrapicus ruber
The Red-breasted Sapsucker occurs in San Diego County in two roles. As a winter visitor it is widespread but uncommon, found mainly in oak and coniferous woodland, as well as in nonnative trees, especially pepper and eucalyptus. In these trees the sapsuckers drill rows of holes, tapping the sap. The scars on the trees last for decades, long after the birds have gone. As a breeding species the Red-breasted Sapsucker is rare and confined to coniferous forest. Curiously, the species is spreading as a breeding bird at the same time the number of winter visitors is shrinking.
Breeding distribution: Breeding Red-breasted Sapsuckers are best known in San Diego County from Palomar Mountain. During the atlas period they were widely distributed on Palomar at elevations from 4600 to 6000 feet with at least 10 pairs. We recorded them on Hot Springs Mountain on eight occasions, with up to four at 5800 to 6000 feet elevation along the road leading north from San Ysidro (F20) 25 May 2001 (M. and B. McIntosh).
The Red-breasted Sapsucker was found for the first time on Volcan Mountain in 2001 with single birds around the south base of the mountain (J20) 7 June (M. B. Stowe) and 15 June (E. C. Hall, J. O. Zimmer).
With 11 reports during the atlas period in the Cuyamaca Mountains, we found the Red-breasted Sapsucker more frequently than expected in that range. All observations were of just one or two birds, except for a family group of four along the Sweetwater River at Hulburd Grove (O19) 4 July 2000 (J. R. Barth). At 3400 feet, this site represents the lowest elevation at which the Red-breasted Sapsucker has been known to breed in San Diego County and the southernmost point of recorded breeding in the species’ entire range. One at Pine Valley (P21) 19 May 2001 (M. B. Mulrooney) was even farther south, also at an unexpectedly low elevation (3680 feet), and also at the lower limit of the pines.
Nesting: Little is yet known of Red-breasted Sapsucker nesting in San Diego County. The two nest sites described by atlas observers were in a black oak and in an ornamental deciduous tree on the grounds of the Palomar Observatory. Our observations of breeding activity imply the birds lay at least from mid May to early June; 13 egg sets from throughout California range from 12 May to 21 June (Bent 1939).
Migration: The Red-breasted Sapsucker occurs as a winter visitor to San Diego County mainly from October through March. Dates of such migrants range from 19 September (1994, one at O’Neill Lake, E6, P. A. Ginsburg) to 29 March, except for three stragglers in May. One was at Point Loma (S7) 5 May 1982 (R. E. Webster, AB 36:894, 1982), one was at Cottonwood Campground (Q25) 6 May 2001 (A. P. and T. E. Keenan), and one was near Deadman Hole (E17) 19 May 2001 (J. D. Barr). The last two were at elevations of 3100 to 4300 feet in oak woodland and may have been pioneers scouting for breeding territories.
Winter: As a winter visitor the Red-breasted Sapsucker is widely but thinly distributed over the county’s coastal slope from sea level to 6000 feet in the mountains. Its numbers in the coastal lowland decrease from north to south. Though the birds feed on a variety of native trees, they are more frequent around some exotic ones, especially the Peruvian pepper. The abundance of pepper trees in the landscaping of the campgrounds at O’Neill Lake and Guajome Lake (G7) accounts for the sapsucker’s being recorded more frequently at these sites than at any others. Our highest daily count in one atlas square in winter, of four on 1 December 1998, was at O’Neill Lake (P. A. Ginsburg).
In the Anza–Borrego Desert the Red-breasted Sapsucker is rare, recorded mainly from exotic planted trees in the Borrego Valley or the cottonwoods planted at Butterfield Ranch (M23). From 1997 to 2002 we noted single individuals in the desert on only six occasions, and only one of these was in native vegetation, the mesquites at Vallecito County Park (14 January 2000, M. C. Jorgensen).
Conservation: Despite its frequent use of ornamental trees, the Red-breasted Sapsucker may be on the decrease as a winter visitor to San Diego County. Numbers on the San Diego Christmas bird count averaged 3.9 per year from 1975 to 1988 but 0.8 per year from 1989 to 2001 and only 0.4 per year from 1997 to 2001. Before 1975 the numbers of the Red-breasted and Red-naped on the count were usually combined and reported as Yellow-bellied. But the average per count of the combined species from 1954 to 1974 was 6.5, so the trend may go back even further. Old sap wells on eucalyptus trees throughout metropolitan San Diego remain as mute testimony to the former widespread occurrence of sapsuckers in an area where we noted only four individual Red-breasteds over the five-year atlas period. Figures from the county’s Christmas bird counts other than San Diego, however, do not show so clear a trend. The species’ winter range could be retracting northward as the trend toward warmer winters compels less migration.
On the other hand, as a breeding bird the Red-breasted Sapsucker is spreading. Early naturalists did not report it in the county in summer; the first record at this season was from Palomar Mountain in 1957 (A. G. Morley in Devillers 1970a). By 1981 there were at least five pairs on Palomar (R. Higson in Unitt 1984). On Hot Springs Mountain I found one on 8 June 1985 but none over three visits in 1980 (Unitt 1981). The first breeding-season reports from the Cuyamaca Mountains were in 1974 (Unitt 1984) and 1983 (C. G. Edwards, AB 37:1028, 1983). It is in these last two areas where the species’ establishment and increase since 1980 have been most noticeable.
Taxonomy: The Red-breasted Sapsucker consists of two subspecies, S. r. ruber (Gmelin, 1788), breeding in the Pacific Northwest, and S. r. daggetti Grinnell, 1901, breeding mainly in California. S. r. daggetti accounts for almost all the winter visitors as well as the breeding population. The one specimen of ruber, from 5 miles northeast of Lakeside 9 November 1957 (SDNHM 30061), is the southernmost of this largely nonmigratory subspecies. Sphyrapicus r. ruber differs from daggetti mainly in its brighter red head (in fresh plumage scarlet rather than crimson), less extensive white head stripe, and smaller yellow-tinged spots on the back.
The Red-breasted, Red-naped, and Yellow-bellied Sapsuckers are closely related, apparently barely over the threshold as species. The Red-breasted and Red-naped hybridize to some extent, chiefly along the eastern flank of the Sierra Nevada, and hybrids have been collected as winter visitors in San Diego County (Devillers 1970a).
Ladder-backed Woodpecker Picoides scalaris
The Ladder-backed Woodpecker is characteristic of desert slopes, the hills and alluvial fans well vegetated with large shrubs like the desert apricot, Mojave yucca, and above all the desert agave. In this habitat the Ladder-backed is an uncommon permanent resident. On the desert floor it is rare, even where there are trees like mesquite and desert ironwood large enough to offer nest sites. Field work for this atlas revealed two areas of semidesert scrub inhabited by Ladder-backed Woodpeckers on the county’s coastal slope, in Dameron and Oak Grove valleys along the Riverside County line, and in Miller Valley on the Campo Plateau.
Breeding distribution: The factor accounting for the Ladder-backed Woodpecker’s distribution in San Diego County is the availability of agaves and yuccas. On desert slopes where these plants are common, the woodpecker is uncommon. Our maximum daily count in one atlas square during the breeding season was eight on the east side of Earthquake Valley (K24) 19 May 2000 (L. J. Hargrove). Rarely, however, did we find more than four. The species ranges as high as 5800 feet elevation in the Santa Rosa Mountains (C27; one bird and one nest hole 4 May 2000, P. Unitt). On the desert floor, or in washes through the badlands, the Ladder-backed Woodpecker is scarce; we found no more than one individual per day in such habitats. Along Fish Creek Wash near the Elephant Knees (M29), we found an old nest hole but never found any birds. Along the western margin of its range, the Ladder-backed Woodpecker drops out as desert-edge scrub merges into chaparral, extending west to Alder Canyon (C21; one on 3 May 2000, G. Rebstock), San Felipe Valley (I21; up to three, including adults feeding young, on 9 June 2000, J. O. Zimmer), and near Bankhead Springs (T27; two on 23 April 2000, P. Unitt).
In addition, the Ladder-backed Woodpecker occurs in two areas of the coastal slope. From the Aguanga region of Riverside County, it extends into north-central San Diego County into Dameron Valley (C15, up to two males 19 April 1997; C16, up to six, including fledglings, 23 June 2001) and even to the north base of Palomar Mountain near High Point Road (C15, two on 14 June 1997, K. L. Weaver).
In Miller Valley (S24) we found the species in 1998, 1999, and 2000, with up to four, including a pair at a nest, 22 June 2000 (L. J. Hargrove). Though on the coastal slope, both Dameron and Miller valleys have many elements of desert biota, such as the cane or snake cholla and white-tailed antelope squirrel.
Nesting: By far the most frequent site for Ladder-backed Woodpecker nests in San Diego County is the flowering stalk of the desert agave. The soft tissue of the stalk is easy for the birds to excavate while the rosette of spine-tipped leaves below offers protection from predators. As atlas observers learned of this preference, they found holes in agaves more often than they found the birds themselves. The woodpeckers also excavate in the other large monocots growing in their habitat, the Mojave yucca and Parry’s nolina. They use true wood, even if dead, only occasionally. We also noted holes in a mesquite snag, a telephone pole, and a railroad trestle. Massey (1998) reported a nest in a gate post. The one nest found in Miller Valley was in a large willow snag.
If the still unknown incubation and nestling periods for the Ladder-backed Woodpecker are the same as the 14 and 15 days, respectively, reported for Nuttall’s (themselves based on minimal data, Lowther 2000a), atlas observations suggest that the Ladder-backed lays at least from late March to late May. Only one egg set was ever collected in San Diego County (6 April). Bent’s (1939) range of 11 April–9 May for all of California was based on only seven records.
Migration: The Ladder-backed Woodpecker is nonmigratory, undertaking short-distance dispersal only. The only well-supported record far from the species’ breeding range is still of one female in the Tijuana River valley (W11) 9 October 1974 (J. L. Dunn, P. Unitt, AB 29:122, 1975). Other reports, such as that of one in Vista 22 July 1982 (AB 36:1017, 1982), were almost certainly based on misidentified juvenile Nuttall’s Woodpeckers, which then gave observers the erroneous impression that the Ladder-backed was resident in the area.
Winter: In winter, the Ladder-backed Woodpecker is seen in its breeding range in much the same numbers as in the breeding season. Our highest daily count in winter was of nine in Box Canyon (L23) 10 January 1998 (S. D. Cameron, S. M. Wolf). Nevertheless, the species does spread to a modest extent in winter; at that season we noted it in 34 squares where we did not find it during the breeding season. These records included four from Oak Grove Valley on the coastal slope, three on the south-facing slopes north of the valley where the species is probably resident, plus one on the south side of the village of Oak Grove (D16; 26 January 2002, R. C. Sanger, K. Williams) where it is a visitor only. On the Campo Plateau, we found the species repeatedly in Miller Valley and also on nine occasions at other scattered locations, west to La Posta Valley (S23; one on 14 February 1999, L. J. Hargrove) and Campo Creek 4.1 miles east-northeast of Cameron Corners (U24; one on 5 January 2001, J. R. Barth).
Conservation: No trends in Ladder-backed Woodpecker numbers in San Diego County are known, though quantitative data from its range are minimal. Most of the species’ habitat is protected within the Anza–Borrego Desert, but development threatens the outlying population in Dameron Valley. A trend toward a drier climate could constrict the woodpecker’s range in the Anza–Borrego Desert but enable it to spread west into new areas. This may be happening already to the north of San Diego County in the San Bernardino Valley (E. A. Cardiff pers. comm.). In May 2000 a pair apparently nested along the Santa Ana River near Mentone, about 18 miles northwest of the traditional edge of the species’ range in San Gorgonio Pass at Banning (D. R. Willick, NAB 54:423, 2000).
Taxonomy: Ladder-backed Woodpeckers throughout southeastern California are P. s. cactophilus Oberholser, 1911, with pale buffy-gray underparts, not distinctly brown as farther south in Baja California.
Hybridization between the Ladder-backed and Nuttall’s Woodpeckers is frequent in Baja California (Short 1971) and regular at some places in Alta California such as Warner Pass and Morongo Valley but rare in San Diego County. The species are segregated by habitat in their narrow zone of overlap, the Ladder-backed in desert-edge scrub on slopes, Nuttall’s in riparian trees in canyon bottoms. L. J. Hargrove suspected that a Ladder-backed in Borrego Palm Canyon 5 July 2001 was paired with a Nuttall’s; G. L. Rogers reported one near Warner Springs (F19) 17 December 2001, well outside the Ladder-back’s breeding range, as a possible hybrid.
Nuttall’s Woodpecker Picoides nuttallii
Nuttall’s is San Diego County’s most widespread woodpecker, a common permanent resident in riparian, oak, and coniferous woodland. And it is spreading farther, colonizing formerly treeless scrub now replaced by urban landscaping. For reasons still not clear, numbers of Nuttall’s Woodpeckers began increasing throughout San Diego County in the late 1980s, and that increase continued through the five-year atlas period.
Breeding distribution: Nuttall’s Woodpecker inhabits almost the entire coastal slope of San Diego County. The population is most concentrated in inland canyons and foothills where the coast live oak is most numerous. The species breeds at all elevations within the county, nearly to the summit of Hot Springs Mountain (E20; up to six, including adults feeding young, 9 June 2001, K. L. Weaver). Otay Mesa, Otay Mountain, and Tecate Peak, along the Mexican border, now form the only extensive area on the coastal slope where Nuttall’s Woodpecker is absent as a breeding bird.
On the desert slope of the mountains, for the most part, the east edge of Nuttall’s Woodpecker range tracks the east edge of the oaks. The birds extend a short distance down slope in canyons with willows. Along Coyote Creek they occur in the breeding season only at Middle Willows on the Riverside County line (C22; three sightings of single birds in April and May, P. D. Jorgensen). They occur also in Borrego Palm Canyon and along San Felipe Creek downstream to the head of Sentenac Canyon (J23; nest with nestlings 2 May 1998, R. Thériault). In southern San Diego County Nuttall’s Woodpecker ranges beyond the oaks to Jacumba (U28) and the mesquite-dominated thicket along Carrizo Creek 2 miles north of Jacumba near Arsenic Springs (T28; one on 30 April and 24 June 1999, J. K. Wilson).
Nesting: Nuttall’s Woodpeckers excavate their nest cavities in dead branches or snags of various trees, preferring the underside of a slanting trunk, a site that enhances protection from predators. Native trees were the most frequently described sites, with willow, sycamore, and oak (both coast live and black) being mentioned six to eight times each, elderberry once. Nonnative vegetation in which atlas observers described Nuttall’s Woodpecker nests included elm (one nest), eucalyptus (two), and, most interestingly, the flowering stalks of Agave americana (three).
The schedule of nesting activity we observed from 1997 to 2001 was consistent with a range of California egg dates of 25 March–18 June (Bent 1939, Sharp 1907). Two early reports of fledglings however, suggest occasional laying as early as mid March (earliest at Oak Hill Cemetery, I12, 16 April 2001, J. O. Zimmer).
Migration: Nuttall’s Woodpecker is nonmigratory, dispersing little outside its breeding range, normally for short distances only. Dates for such dispersers in the Anza–Borrego Desert range from 10 August (2000, one at Lower Willows along Coyote Creek, D23, P. D. Jorgensen) to 20 February (1978, one at the same location, B. Cord).
Winter: We noted Nuttall’s Woodpecker in 17 atlas squares where it probably does not breed. Almost all of these, however, were adjacent to squares where it probably does. Farthest afield were one in upper Barton Canyon, Santa Rosa Mountains (C27), 9 January 2002 (P. Unitt), three on the floor of the Borrego Valley in Borrego Springs (F24/G24; two on 19 December 1999, P. K. Nelson, P. D. Ache; one on 16 December 2001, R. Thériault), and two at Vallecito County Park (M25; 2 December 2000, P. Unitt; 25 February 2001, J. R. Barth).
Conservation: Before the mid 1980s Nuttall’s Woodpecker was confined in San Diego County to native woodlands almost exclusively. Even in well-wooded Balboa Park it was a only rare winter visitor. Since then, however, it has spread widely into cities, taking advantage of woodpecker-friendly trees like Liquidambar, birch, white alder, and even Agave americana. The average on San Diego Christmas bird counts has increased tenfold from 2.9 from 1953 to 1988 to 29.6 from 1997 to 2001 (maximum 48 in 2001).
The maturation of large numbers of urban trees is an attractive hypothesis that may help explain Nuttall’s Woodpecker increase and spread. Nevertheless, some other forces still to be identified must be operating as well. Numbers on the Oceanside, Rancho Santa Fe, Escondido, and Lake Henshaw Christmas bird counts have all increased as well, if not so dramatically as at San Diego. On the Escondido count, for example, well within the woodpecker’s traditional range, the average per count increased by a factor of 2.6 from 1985–89 to 1997–2001. Even when corrected by number of party-hours the factor of increase was 2.3. The Breeding Bird Survey (Sauer et al. 2003) has not revealed any such increase covering the species’ range in general.
Whatever the reason for Nuttall’s Woodpecker increase, it opens an opportunity for increases in other small birds that nest in its used holes, such as the House Wren, Western Bluebird, and White-breasted Nuthatch.
Downy Woodpecker Picoides pubescens
Among San Diego County’s more interesting bird stories is that of the Downy Woodpecker. There were a few records, including breeding, before the early 1970s, but by that time the woodpecker was essentially a lost species. In the late 1970s it was found locally in northwestern San Diego County, then in the 1980s it spread abruptly throughout the coastal lowland. Currently it is an uncommon but widespread resident of riparian woodland and gradually spreading inland to ever higher elevations.
Breeding distribution: The Downy Woodpecker’s center of distribution remains the riparian woodlands of northwestern San Diego County, where daily counts in one atlas square are as high as six (along the San Luis Rey River near Gird Road, E8, 21 and 26 March, 26 April, and 9 July 1999, P. A. Ginsburg). In this region the birds have moved beyond the main rivers to colonize many subsidiary creeks with willow thickets. In the southern half of the county the Downy Woodpecker still occurs mainly along the principal watercourses: Los Peñasquitos Canyon, the San Diego River, the Sweetwater River, the Otay River, and the Tijuana River. The most inland sites where the species is known during the breeding season are Temecula Creek near Oak Grove (C16; up to four on 20 June 1998, K. L. Weaver), the San Luis Rey River near Puerta La Cruz (E18; two on 18 June 2000, J. K. Wilson, P. K. Nelson), Warner Springs (F19; one on 3 May 1999, C. G. Edwards), the San Luis Rey River near the Forest Service picnic ground (G16; up to two, a pair, on 3 July 1999, W. E. Haas), Witch Creek (J18; female with two fledglings 12 July 1999, S. E. Smith), Hatfield Creek 3.2 miles east of Ramona (K16; pair at nest 11 June 2000, L. J. Hargrove), Sweetwater River above Loveland Reservoir (Q17; one on 21 May 1999, P. Famolaro), and Marron Valley (V17; four on 12 June 2000, P. P. Beck).
The records along the Mexican border, in Marron Valley and the Tijuana River valley (W11; up to three, including a fledgling, 19 June 1999, P. Unitt) are notable because the Downy Woodpecker is not known to breed in Mexico. By 2001 there were only four well supported records from Baja California, all from November through February (Erickson et al. 2001; M. A. Patten).
Nesting: In San Diego County, the Downy Woodpecker nests typically in willow snags. Dates of breeding activity observed suggest egg laying from mid April to mid June; Bent (1939) gave 7 April–9 June as the range for 82 California egg sets.
Migration: The Downy Woodpecker is nonmigratory, but there must be considerable dispersal for the species to have spread so rapidly. Some, perhaps most, of this is done by the young soon after fledging. A juvenile found dead in the Fletcher Hills area of El Cajon (Q12) 14 June 1998 (C. Tratnyek, SDNHM 50417) was crossing unsuitable habitat. Other records of apparent dispersers or pioneers away from breeding sites are of single birds at Point Loma (S7) 12 April 1986 (R. E. Webster, AB 40:524, 1986) and 22 May 2001 (P. A. Ginsburg), one in the Hillcrest area of San Diego (R9) 25 July 2001 (P. Unitt), one at Lake Henshaw (G17) 17 July 1998 (C. G. Edwards), and one near Julian (J20) 17 August 2000 (M. B. Stowe). At 4000 feet, the last, and one at 4650 feet at Lake Cuyamaca (M20) 11 March 1988 (C. G. Edwards), were at the highest elevations where the Downy Woodpecker has yet been recorded in San Diego County.
Winter: Our winter observations of the Downy Woodpecker included several in marginal or atypical habitat, suggesting further pioneering. Such birds included individuals at 2650–3350 feet elevation along the San Luis Rey River between Lake Henshaw and Puerta La Cruz (F18) 10 December 2000 (J. R. Barth, M. Mathos), at Mesa Grande (H17) 17 December 2001 (K. L. Weaver, J. McColm), and, most notably, one a short distance onto the desert slope in San Felipe Valley (I21) 3 December 2000 (W. E. Haas).
Conservation: In the first half of the 20th century the Downy Woodpecker was rare in San Diego County but recorded at Bonsall, the head of Lake Hodges (eggs collected, WFVZ), San Pasqual (“rather rare,” eggs collected, Sharp 1907), 2–3 miles northeast of Old Mission Dam, and 2 miles northeast of Lakeside (Short 1971). Then the species evidently declined almost to extirpation: in the 1950s and 1960s there were only two records. In the 1970s it was absent from the San Pasqual and Old Mission Dam areas but present in small numbers along and near the Santa Margarita and lower San Luis Rey rivers (Unitt 1984). From 1981 on the Downy Woodpecker could be found consistently along the San Diego River. It was first noted in the Tijuana River valley 25 September 1983 (C. G. Edwards, AB 38:247, 1984), and by 1990 it was resident there. Since then the Downy Woodpecker has been filling in by colonizing smaller patches of riparian woodland and spreading inland. It was found on only one San Diego Christmas bird count before 1986, but since then it has been found annually, the numbers increasing gradually, reaching 10 on 15 December 2001.
The Downy Woodpecker’s reversal of fortune in San Diego County seems counterintuitive for a species dependent on riparian woodland, so much of which has been degraded and removed. A possible factor is the damming of most rivers and creeks, stabilizing the riparian environment in a way it never experienced previously. Under natural conditions winter floods knock over trees and perhaps prevent many from growing to maturity and developing enough dead snags for nest sites. Now such flooding has been greatly reduced, allowing more trees to live to maturity and senility. Changing land use has allowed riparian woodland to regenerate in some areas, such as the Tijuana River valley, where it was absent in the 1960s.
Some other subtle factors may be at work, too. The Downy Woodpecker may be benefiting from whatever causes are enabling the Nuttall’s Woodpecker to spread also. The southward spread of the Downy Woodpecker parallels that of some other species of similar habitats, especially the Western Flycatcher and Orange-crowned Warbler.
Taxonomy: Downy Woodpeckers in San Diego County, as in most of cismontane California, are P. p. turati (Malherbe, 1860), small with the underparts lightly tinged smoke-gray. In the field, the difference from white is difficult to appreciate in spring and summer when the birds are in worn plumage and more or less stained from months of contact with trees, but it can be seen in a good view in fall and winter when the birds are clean and fresh.
Hybrids between the Downy and Nuttall’s Woodpeckers continue to turn up occasionally, as 2.3 miles northeast of Bonsall 7 May 1984 (SDNHM 43956, Unitt 1986) and in the Tijuana River valley 25 February 1984 (G. McCaskie, AB 38:358, 1984) and 5 December 2000 (P. Unitt).
Hairy Woodpecker Picoides villosus
The Hairy Woodpecker’s sharp call, like a rubber squeeze-toy, is a characteristic sound of coniferous forests in San Diego County’s mountains. The species is an uncommon year-round resident in this habitat. Only a few individuals spill over into nearby oak-dominated woodland with few or no conifers. Winter vagrants far from the breeding range are very rare. But the Hairy Woodpecker also occurs irregularly at low elevations in the breeding season, mainly in the county’s northwestern corner.
Breeding distribution: During the breeding season, atlas results show a close correspondence between the Hairy Woodpecker and San Diego County’s coniferous forests. The highest counts per day are of only six, as on Hot Springs Mountain (E20) 27 June 2001 (K. L. Weaver, C. R. Mahrdt) and in the Cuyamaca Mountains (M20), on Middle Peak 11 June 2000 (R. E. Webster) and on Cuyamaca Peak 13 July 2000 (J. R. Barth). In the southern half of the county the Hairy Woodpecker breeds down to about 3800 feet elevation, but around Palomar Mountain it breeds locally even lower, down to 2470 feet along the San Luis Rey River (F16; pair nesting June–July 2000 and 2001, W. E. Haas) and about 1600 feet in Marion Canyon (D12; one agitated 18 June 2001, K. L. Weaver). Some outlying locations for the species are Bucksnort Mountain (C20; up to two on 24 June 2000, L. J. Hargrove) and Corte Madera Mountain (R20; one on 20 June 1998, P. Unitt).
The Hairy Woodpecker occurs in the breeding season rarely and irregularly in lowland riparian and oak woodland in northwestern San Diego County. Otherwise, the species’ lowland distribution extends south to the Santa Ana River valley in northwestern Riverside County (Garrett and Dunn 1981, Gallagher 1997). On 28 June 1998, an adult was feeding a fledgling along the Santa Margarita River near Rifle Range Road (F5; R. E. Fischer)—the southernmost confirmation of the Hairy Woodpecker nesting at low elevation along the Pacific coast. At Los Jilgueros Preserve, Fallbrook (D7), there was a single individual on 21 January and 7 May 1998 (E. Ashton). In 1983, Scott (1984) found two territories and one nest in riparian woodland along the Santa Margarita River at De Luz Creek (D6); in 1989 Weaver (1990) found one territory in coast live oak woodland in the Santa Margarita Ecological Reserve (C9). At a mere 850–900 feet, though only about 6 miles west of the species’ normal habitat, was a single Hairy Woodpecker along the San Diego River between Cedar and Boulder creeks 21 March and 6 June 1998 (R. C. Sanger).
Nesting: The Hairy Woodpecker excavates a typical woodpecker hole in a tree, commonly a dead snag, but atlas observers found few nests in San Diego County. One nest on Hot Springs Mountain was about 25 feet above the ground. The nest along the San Luis Rey River was in a sycamore, an atypical site for the species in southern California. Our rather meager records of breeding activity range from an occupied nest on 10 May to young fledging in the third week of July and fledglings out of the nest on 29 July. These dates suggest egg laying at least from mid May to early June, well within the range of 23 March–21 June given for 43 California egg sets by Bent (1939).
Migration: The few records of Hairy Woodpeckers outside their breeding range in San Diego County are scattered from 27 August (1988, one in the Tijuana River valley, B. E. Daniels, AB 43:169, 1989) to 26 February (1980, one at Old Mission Dam, P11, C. G. Edwards).
Winter: The Hairy Woodpecker remains in its breeding range year round. Our highest daily count in winter was of four around Mount Laguna Mountains (O23) 21 January 2002 (E. C. Hall, J. O. Zimmer). The species has been noted outside its known breeding range in San Diego County on about 25 occasions. During the atlas period the one farthest from the usual range was at Olivenhain (K8) 28 December 1997 (L. R. Santaella), but earlier records extend as far as Otay Valley (V11; one from 15 December 1979 to 26 January 1980, AB 34:307, 1980; one on 15 December 1990, P. Unitt) and the Tijuana River valley (cited above). There are only two records from the Anza–Borrego Desert, of one in pines planted on a golf course in Borrego Springs (F24) 21 December 1991 (M. L. Gabel) and one in pinyons between 4800 and 5000 feet in the Santa Rosa Mountains 1.6 miles east-southeast of Villager Peak (D27) 9 January 2002 (L. J. Hargrove). The latter had probably dispersed along the ridge from more heavily wooded areas of the Santa Rosa Mountains in Riverside County, where the species is resident.
Conservation: Data sufficient to demonstrate any trend in the Hairy Woodpecker’s status in San Diego County do not exist. Anecdotal observations suggest no significant change. On 26 May 1976 A. Fries noted two at Mesa Grande (H17), an area of oak woodland where we found none during the atlas period; the species could be irregular in this area.
Taxonomy: The Hairy Woodpeckers resident in San Diego County are P. v. hyloscopus (Cabanis and Heine, 1863), in which the whitish underparts are lightly tinged buffy-gray. Long-distance vagrancy of Hairy Woodpeckers is unknown in California, yet the one specimen from outside the breeding range in San Diego County, from Cottonwood Campground (Q25) 19 January 1985 (SDNHM 43460), has conspicuously whiter underparts than any specimen of hyloscopus. It matches specimens of P. v. orius (Oberholser, 1911), which breeds from south-central British Columbia south to Arizona, including the Sierra Nevada and mountains of the Great Basin, if P. v. leucothorectis (Oberholser, 1911) is considered a synonym of orius (Phillips et al. 1964, Short 1982).
White-headed Woodpecker Picoides albolarvatus
In San Diego County, which represents the southern tip of its range, the White-headed Woodpecker is uncommon to rare, breeding only in coniferous forest near the mountain tops. Even here it occupies only a fraction of the habitat, occurring mainly where the sugar pine is an important constituent of the forest. Only twice have vagrants been recorded in San Diego County away from the mountains.
Breeding distribution: The White-headed Woodpecker is most numerous on Hot Springs Mountain; in places there it can be the most conspicuous woodpecker (up to eight, representing probably five pairs, east of the summit, E21, 19 June 1999, K. L. Weaver, C. R. Mahrdt). On the south side of the mountain it is found only above 5800 feet elevation, but on the north side it extends down to the mountain’s base, occurring down to 4600 feet in Lost Valley (D20/D21; up to three on 28 April 2000, W. E. Haas). On Palomar Mountain, the White-headed Woodpecker occurs mainly around the observatory (D15; up to three, including a pair, on 18 April 1998, K. L. Weaver). In Palomar Mountain State Park (D14) only a single individual was noted during the breeding season from 1997 to 2001, on 2 June 1998 (P. D. Jorgensen). On Volcan Mountain (I20), the species is rare, occurring above 5300 feet elevation (five, including a family group, 16 July 2001, J. R. Barth). In the Cuyamaca Mountains, the White-headed Woodpecker is uncommon above 5300 feet elevation on North Peak (L20), Middle Peak (M20; maximum daily count three on 2 July 2000, R. E. Webster), and Cuyamaca Peak (M20/N20). In the Laguna Mountains, the White-headed Woodpecker is rare and confined to the vicinity of Al Bahr Shrine Camp (O23); the highest number reported there, seven on 9 and 10 June 2001, was spread over two days so may have entailed some double counting (C. G. Edwards). One on 4 June 2001 along the trail to Garnet Peak about 1.4 miles north-northwest of Al Bahr Shrine Camp (N23; K. J. Winter) was the most distant from that site.
Nesting: Like other woodpeckers, the White-headed excavates its own nest hole, usually in a dead snag. A pair on Hot Springs Mountain (F21) was excavating a nest cavity 29 May 1999 (J. M. and B. Hargrove). Atlas observers noted the birds carrying food items from 25 May to 16 July. These dates suggest egg laying at least from mid May to early June, well within the range of 24 April–16 June for 53 California egg sets given by Bent (1939).
Winter: The White-headed Woodpecker is essentially sedentary, seen in winter in the same places in much the same numbers as during the breeding season. During the atlas period our highest winter count was of five on Hot Springs Mountain (E21) 11 December 1999 (K. L. Weaver, C. R. Mahrdt). The addition of atlas square E14 as a winter location resulted from one bird seen at Observatory Campground, just 1.2 miles southwest of the Palomar Observatory, 24 February 1999 (G. L. Rogers). The only winter record from the Laguna Mountains during the atlas period was of one at the north end of Big Laguna Lake (O23) 6 December 1999 (D. S. Cooper).
Of California’s high-mountain birds, the White-headed Woodpecker is one of the least inclined to vagrancy. San Diego County’s only winter records more than about 2 miles from breeding localities are of one at Ramona (K15) 20 November 1955 (AFN 10:58, 1956) and one male in planted pines at the Cottonwood Fire Station, at 3080 feet elevation northeast of Lake Morena (S22), 27 February 2000 (R. Breisch). The last made the species’ southernmost record ever. The winter of 1955–56 was an invasion year for several species of mountain birds, but that of 1999–2000 was not.
Conservation: San Diego County’s small population of the White-headed Woodpecker may be decreasing slowly. My count of 13 on Hot Springs Mountain 23–24 June 1980 (Unitt 1981) was not equaled from 1997 to 2002. During the atlas period the species was reported less frequently and from fewer locations on Palomar Mountain than before 1980. We did not find it at William Heise County Park (K20), where it occurred in the 1970s (Unitt 1984). The woodpecker’s habitat in San Diego County covers under 4 square miles on Hot Springs Mountain, less in the other ranges. Thus it is vulnerable to factors like extended droughts, forest fires, and irruptions of bark beetles killing pine trees. Logging, silviculture, and fire suppression are thought responsible for the White-headed Woodpecker’s decline in Washington, Oregon, and Idaho (Garrett et al. 1996).
Taxonomy: White-headed Woodpeckers in San Diego County belong to the large-billed subspecies P. a. gravirostris Grinnell, 1902.
Northern Flicker Colaptes auratus
San Diego County’s largest woodpecker is a fairly common resident in coniferous forest, oak woodland and sycamore groves. Though it nests in tree cavities like other woodpeckers, it feeds largely on the ground, specializing on ants. The local population is much augmented in winter by migrants from the north, which occur in the same habitats as the residents, as well as invading grassland, desert, and developed areas where breeding flickers are few or none.
Breeding distribution: The pattern of flicker abundance in San Diego County resembles that of many other oak woodland birds: the birds are most numerous in the mountains and foothills, and they extend toward the coast more commonly in the north than in the south. In the core range, daily counts in the breeding season range up to 15 at Mount Laguna (O23) 24 July 1998 (E. C. Hall), 15 at Wynola (J19) 22 May 1999 (S. E. Smith), and 17 at De Luz (B6) 20 June 2000 (K. L. Weaver). An area outside the core where flickers are especially common, with its abundant oaks and sycamores, is Los Peñasquitos Canyon (N8/N9), with up to 18 on 1 April 2001 (N8; B. Siegel). In south-coastal San Diego County breeding flickers are uncommon to rare, with no count of over three per day from mid April through August. On the east slope of the mountains, the edge of the flicker’s range follows the edge of the oaks closely, though the birds occur also in riparian woodland at Scissors Crossing (J22; courting pair 13 April 1998, E. C. Hall), in planted cottonwoods at Butterfield Ranch (M23; occupied nest hole 17 April 1999, P. K. Nelson; pair with fledgling 18 June 1999, H. and. K. Williams), and along Carrizo Creek north of Jacumba (T28; one on 3 May 1998 and 11 May 2001, F. L. Unmack).
Nesting: Flickers excavate their nest holes typically in dead trees or dead snags of living trees but sometimes in live trunks or branches. The most frequent nest site described by atlas observers was coast live oak; willows, cottonwoods, and sycamores were also mentioned. A flicker in Johnson Canyon on the north slope of Otay Mesa (V13) 1 April 2000 was attending a hole in a dead eucalyptus (P. Unitt); no suitable native trees were in the area. Another nest was in a telephone pole along the Santa Margarita River at De Luz Road (C7) 11 April 1998 (K. L. Weaver).
The nesting schedule we observed from 1997 to 2001 was largely consistent with the 9 April–20 June range of 33 egg sets collected in San Diego County 1894–1945. A fledgling near Dyche Valley (F15) 5 May 1997 (M. Dougan) suggests egg laying about 1 April.
Migration: Migrant flickers occur in San Diego County mainly from October through March. Specimens attest to dates from 2 October to 2 April (see under Taxonomy). The earliest date of a sight report away from a breeding locality is 15 September (1973, one in Tubb Canyon, H23; one at Borrego Palm Canyon campground, F23), except for one at Tamarisk Grove (I24) 20 August 1984 (B. Knaak, ABDSP database). Probably sightings before the last week of September represent short-distance dispersal of the local population, not the arrival of migrants from farther north. In spring, records after the first week of April are few. The only reports later than 24 April are of one at Angelina Spring (I22) 2 May 1997 (P. K. Nelson) and one at Agua Caliente Springs (M26) 4 June 1998 (E. C. Hall).
Winter: In winter, the flicker is more common than in the breeding season, with daily counts up to 30 near the Pine Hills Fire Station (L19) 6 February 1999 and 35 in the Wooded Hill/Morris Ranch area of the Laguna Mountains (P23) 19 February 1999 (E. C. Hall). Winter visitors spread over the whole coastal slope, including areas where the species does not breed (up to nine in the southeast quadrant of the Tijuana River valley, W11, 5 December 2000, P. Unitt). Wintering flickers also reach the Anza–Borrego Desert, occurring mainly at oases and around the trees planted in Borrego Springs (F24; up to 17 on 20 December 1998, R. Thériault et al.).
Conservation: The Northern Flicker both benefits and suffers from man-made changes in the environment. The planting of trees in what was once treeless scrub has enabled the species to colonize areas like Point Loma and Chula Vista, where it was doubtless absent as a breeding bird before urbanization. The regeneration of riparian woodland may be allowing the flicker to colonize the Tijuana River valley, where it was not known in the breeding season before 2000 (one in Goat Canyon, W10, 13 and 23 May 2000, W. E. Haas). The number of flickers using these novel habitats, however, is very small. On the negative side, the proliferation of the European Starling has been blamed for a decline of flickers over much of North America. Cities offer little opportunity for foraging to a bird like the flicker that feeds primarily in the dirt. From 1997 to 2001, the number of flickers on the San Diego and Oceanside Christmas bird counts was barely over half what it was from the mid 1960s through 1970s, probably as a result of the urbanization of the count circles.
Taxonomy: The subspecies of flicker resident in San Diego County is C. a. collaris Vigors, 1829, a Red-shafted Flicker with the nape and crown the same dark brown color as the back. It breeds along the Pacific coast from northern California to northern Baja California. In winter collaris is outnumbered by C. a. canescens Brodkorb, 1935, which is often paler on the back than collaris and has the nape and crown grayer. It breeds inland from the Sierra Nevada to the Rocky Mountains and occurs in San Diego County as a winter visitor at least from 2 October (1981, Clairemont area of San Diego, P8, SDNHM 41613) to 2 April (1988, Chula Vista, U11, SDNHM 47783).
The Yellow-shafted Flicker is a rare winter visitor to San Diego County. Three were reported during the atlas period (one along the Sweetwater River near Highway 94, R13, 3 January 2000; one in Mission Gorge, P11, 8 January 2000, D. Kisner; one in Thing Valley, Q24, 25 December 2001, J. R. Barth), and other flickers with some but possibly not all of the characters of the Yellow-shafted were also noted. One specimen (Point Loma, 15 February 1954, SDNHM 30001) shows all the features of a Yellow-shafted; it is of the large northern subspecies C. a. luteus Ridgway, 1911. Several specimens of canescens have just one feature of the Yellow-shafted, either yellowish shafts or red in the nape. Sight records of Yellow-shafted Flickers extend from 4 October (1973, Point Loma, G. McCaskie) to 4 April (1978, Point Loma, AB 32:1056, 1978).